Method of pulling a single crystal

ABSTRACT

PCT No. PCT/JP97/03015 Sec. 371 Date Dec. 9, 1999 Sec. 102(e) Date Dec. 9, 1999 PCT Filed Aug. 29, 1997 PCT Pub. No. WO98/09007 PCT Pub. Date Mar. 5, 1998A method of pulling a single crystal includes forming an enlarged portion 26b and a reduced portion 26c under a neck 26a, and fitting the reduced portion for pulling an upsized single crystal. The reduced portion is formed with angle  theta s so that the diameter can be measured at all times using an optical measuring means 19 with optical axis angle  theta m, such that  theta s&gt; theta m.

TECHNICAL FIELD

The present invention relates to a method of pulling a single crystaland, more particularly, to a method of pulling a single crystal whereina single crystal of silicon or the like is pulled from a melt of amaterial for forming a single crystal by a pulling method such as theCzochralski method (hereinafter, referred to as the CZ method).

BACKGROUND ART

At present, the majority of silicon single crystals used formanufacturing a substrate for forming a circuit component of a LSI(large scale integrated circuit) and the like have been pulled by the CZmethod. FIG. 1 is a diagrammatic sectional view of a conventionalapparatus for pulling a single crystal using the CZ method. In thefigure, reference numeral 21 represents a crucible.

The crucible 21 comprises a bottomed cylindrical quartz crucible 21a anda bottomed cylindrical graphite crucible 21b fitted on the outer side ofthe quartz crucible 21a. The graphite crucible 21b is fitted in agraphite fitting part 28a. The crucible 21 and the fitting part 28a aresupported with a support shaft 28 which rotates in the direction shownby the arrow A in the figure at a prescribed speed. A heater 22 of aresistance heating type and a heat insulating mold 27 arranged aroundthe heater 22 are concentrically arranged around the crucible 21. Thecrucible 21 is charged with a melt 23 of a material for forming acrystal which is melted by the heater 22. On the central axis of thecrucible 21, a pulling axis 24 made of a pulling rod or wire issuspended, and at the lower end thereof, a seed crystal 35 is held by aholder 34a. These parts are arranged within a water cooled type chamber39 wherein pressure can be controlled, while an optical measuring means19 is arranged above the crucible 21 outside the chamber 39.

In pulling a single crystal 36 using the above-mentioned apparatus forpulling a single crystal 30, the pressure in the chamber 39 is reducedand an inert gas is introduced into the chamber 39 so as to make aninert gas atmosphere under reduced pressure, which is maintained for aperiod of time. Then, the material for forming a crystal is melted bythe heater 22.

While the pulling axis 24 is rotated on the same axis in the reversedirection of the support shaft 28 at a prescribed speed, the seedcrystal 35 held by the holder 34a descends and is brought into contactwith the melt 23, and the pulling of the single crystal 36 from the melt23 is started. When the crystal is made to grow at the lower end portionof the seed crystal 35 as the pulling is carried out, the crystal isonce narrowed down to have a prescribed diameter, leading to theformation of a neck 36a (hereinafter, referred to as the necking step).

After forming a shoulder 36b by making the neck 36a grow to have aprescribed diameter, a main body 36c having a uniform diameter and aprescribed length is formed. The diameter of the single crystal 36 isgradually decreased and the temperature of the whole single crystal 36is gradually lowered, leading to the formation of an end-cone. Then, thesingle crystal 36 is separated from the melt 23. Here, in the abovesteps, the diameter of the single crystal 36 is measured by measuringluminance of the growth interface (fusion ring) on the surface of themelt 23 when the single crystal 36 is formed, using the opticalmeasuring means 19, and is controlled on the basis of the results.

In the above conventional method for pulling a single crystal, the neck36a is formed under the seed crystal 35 in order to exclude thedislocation induced by a thermal shock when the seed crystal 35 isbrought into contact with the melt 23. Ordinarily, the neck 36a has adiameter of 3 mm or so and a length of 30 mm or so. In pulling a singlecrystal 36 having a diameter of about 6 inches and a weight of 80 kg orso, even the neck 36a having the above diameter can sufficiently supportthe pulled single crystal 36.

Recently, however, in order to manufacture a more highly integratedsemiconductor device at a lower cost and more efficiently, the wafer hasbeen required to have a larger diameter. Now, for example, theproduction of the single crystal 36 having a diameter of about 12 inches(300 mm) and a weight of 300 kg or so is desired. In this case, the neck36a having a conventional diameter(usually 3 mm or so) cannot withstandthe weight of the pulled single crystal 36 and breaks, resulting in thefailing of the single crystal 36.

In order to solve the above problem, a method for pulling a singlecrystal has been disclosed. The diameter of the single crystal isgradually enlarged once under the neck to form an enlarged portion. Thediameter of the crystal is gradually reduced to form a reduced portionhaving a larger diameter than the neck, which is supported by asupporting apparatus when the single crystal is pulled.

FIG. 2 is a diagrammatic sectional view of a conventional apparatus forpulling a single crystal including such kind of single crystalsupporting apparatus (Japanese Patent Publication No.515/95), and in thefigure, reference numeral 51 represents a crucible.

The bottom, almost cylindrical crucible 51 is charged with a melt 53 ofa material for forming a single crystal. A pulling wire 41a is suspendedabove the crucible 51, and is caused to move up and down and to rotatein the direction shown by the arrow A by a wire actuator 47. To thelower end portion of the pulling wire 41a, a bar-shaped pulling axis 41bis joined, around which a pipe-shaped rotor 42 is arranged by a bearing42a so as to be rotatable. To the upper portion of the pulling axis 41b,a motor 43 is fitted, and the motor 43 is connected to the upper portionof the rotor 42 and is electrically joined to a receiving portion 43a.When a signal transmitted from the outside of a chamber (not shown) ofan apparatus for pulling a single crystal 40 using a transmitting means(not shown) is received by the receiving portion 43a, the motor 43 isdriven so as to rotate the rotor 42 in the direction shown by the arrowB or C. On the outer regions of the rotor 42, an external thread portion42b is formed, to which a disc-shaped supporting portion 44a is screwed.From the lower portion of the supporting portion 44a, a cylindricalgrasping holder 44b is extended, and on the inner surface thereof, guideslots 44c are vertically formed so as to face each other. In the lowerportion of the grasping holder 44b, plural notches 44d are formed, inwhich pawls 44e are pivoted so as to be rotatable. At the lower endportion of the grasping holder 44b, a stopper portion 44f is formed.Accordingly, the pawls 44e can turn upward, while they are inhibitedfrom turning downward by the stopper portion 44f. A grasping means 44includes the supporting portion 44a, grasping holder 44b, pawls 44e,stopper portion 44f, and associated parts. On the other hand, a holder41c is connected to the lower end portion of the pulling axis 41b, and aflange 45 is fixed to the outer regions of the holder 41c. The outerregions of the flange 45 are fitted in the guide slots 44c so as toslide up and down. When the rotor 42 rotates, the grasping means 44moves up and down as the rotation thereof is restricted. A singlecrystal supporting apparatus 40a includes the pulling axis 41b, rotor42, motor 43, grasping means 44, flange 45, and associated parts. At thelower end portion of the holder 41c, a seed crystal 41d is held.

In pulling a single crystal 46 using the apparatus for pulling a singlecrystal 40 having the above construction, the motor 43 is driven in thenormal direction of rotation so as to rotate the rotor 42 (for example,in the direction of the arrow B) and to transfer upward the graspingmeans 44 which is screwed thereto. The wire actuator 47 is driven so asto transfer the holder 41c downward through the pulling wire 41a andpulling axis 41b to dip the seed crystal 41d into the melt 53. The wireactuator 47 is driven so as to pull the pulling wire 41a with rotationat a relatively high speed, leading to the formation of a neck 46a. Bypulling the pulling wire 41a away from the melt at a gradually decreasedspeed, an enlarged portion 46b having a large diameter is formed underthe neck 46a. By pulling the pulling wire 41a at a relatively high speedagain, a reduced portion 46c having a smaller diameter than the enlargedportion 46b is formed under the enlarged portion 46b. By pulling thepulling wire 41a at a gradually decreased speed, a shoulder portion 46dis formed under the reduced portion 46c. At that time, by transmitting asignal to the receiving portion 43a using the above transmitting means,the motor 43 is driven in the reverse direction of rotation so as torotate the rotor 42 in the direction of the arrow C to transfer thegrasping means 44 downward. When the pawls 44e touch the enlargedportion 46b, the pawls 44e are caused to turn relatively upward so as toavoid the enlarged portion 46b and are fitted to the reduced portion46c. When the pulling wire 41a is pulled at a prescribed speed after themotor 43 is stopped, a main body 46e having a prescribed diameter isformed under the shoulder portion 46d where the reduced portion 46c isheld by the single crystal supporting apparatus 40a.

To separate the grown single crystal 46 from the melt 53, the pullingwire 41a is pulled at a relatively high speed so as to gradually reducethe crystal diameter to form an inverse conical crystal tail (notshown), and the single crystal 46 is separated from the melt 53 at apoint of time when the single crystal 46 has a sufficiently smalldiameter to prevent dislocation from propagating to a product portioneven if the dislocation occurs. This step has been adopted in order toprevent the dislocation from being caused by a thermal shock and frompropagating to the main body 46e which forms the product portion.

The above apparatus for pulling a single crystal 40 makes it possible topull an upsized single crystal 46. However, when the diameter iscontrolled using the optical measuring means 19 in the same manner as inthe case using the conventional apparatus for pulling a single crystal30, the growth interface is hidden by the enlarged portion 46b in theformation of the reduced portion 46c, so that the fusion ring cannot beobserved. Therefore, it is difficult to control the diameter of thesingle crystal 46 using the optical measuring means 19 in the formationof the reduced portion 46c, and, thus, it is difficult to form thereduced portion 46c having a prescribed shape. Since it is difficult tocontrol the shape of the reduced portion 46c, it is difficult to copewith changes in the conditions such as the temperature of the melt 53,so that dislocation is easily induced to the reduced portion 46c.

The conventional apparatus for pulling a single crystal 40 (FIG. 2) bywhich the single crystal 46 is pulled as the reduced portion 46c isheld, has a complicated structure. Since the complicated single crystalsupporting apparatus 40a must be arranged in a high temperatureatmosphere just above the melt 53, troubles are easily caused.

Another apparatus for pulling a single crystal has been disclosed. Inthis apparatus, a structure for holding a reduced portion and a pullingaxis for pulling a single crystal individually ascend and descend.However, in such apparatus, it is difficult to synchronize theascent/descent speed and the number of revolutions, and it is alsodifficult to certainly hold a single crystal when the central axis evenslightly slips out of place.

Since the single crystal supporting apparatus 40a, forming part of theapparatus for pulling a single crystal 40, has a construction whereinthe reduced portion 46c is grasped by the pawls 44e, the fittingstrength is small and the pawls 44e are easy to break.

SUMMARY OF THE INVENTION

The present invention was developed in order to solve the aboveproblems. It is object of the present invention to provide a method ofpulling a single crystal, wherein the diameter can be stably controlledin the formation of a reduced portion of a single crystal.

In order to achieve this object, a method of pulling a single crystalaccording to the present invention is provided. A single crystal ispulled as the diameter thereof on the melt interface is measured usingan optical measuring means arranged above a crucible. Thus, the diameterof the crystal can be controlled. This method includes a necking stepwherein a neck is formed under a seed crystal by rotating the seedcrystal after dipping the seed crystal into the melt within thecrucible. The method further includes an enlarged portion formation stepwherein the diameter of the single crystal is gradually increased onceafter the necking step, and a reduced portion formation step wherein thediameter of the single crystal is gradually reduced after the enlargedportion formation step so as to form a reduced portion. Thus, theinstant method is particularly characterized by forming the reducedportion so that the relationship θ_(s) >θ_(m) holds when the opticalaxis of the optical measuring device and a horizontal plane make anangle θ_(m), and when a straight line forming the surface of the reducedportion and a horizontal plane make an angle θ_(s). In addition, thediameter of the reduced portion is measured at all times using theoptical measuring means.

In the method of pulling a single crystal the diameter is measured atall times through the fusion ring in the formation of the reducedportion, so that the shape of the reduced portion can be controlledprecisely. Therefore, it is possible to accurately cope with even achange in the temperature of the melt or the like. As a result,dislocation is not induced in the formation of the reduced portion, sothat a single crystal containing no fault such as dislocation can bepulled from the melt.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagrammatic sectional view showing a conventional apparatusfor pulling a single crystal;

FIG. 2 is a diagrammatic sectional view showing another conventionalapparatus for pulling a single crystal;

FIG. 3 is a longitudinal sectional view diagrammatically showing anapparatus for pulling a single crystal according to an embodiment of thepresent invention;

FIG. 4 is a partial sectional side view diagrammatically showing asingle crystal holding means which forms part of the apparatus forpulling a single crystal and the vicinity thereof according to theembodiment;

FIG. 5 is a sectional view along line V--V of FIG. 4;

FIG. 6 is a plan view diagrammatically showing the single crystalholding means which forms part of the apparatus for pulling a singlecrystal according to the embodiment;

FIG. 7 is a longitudinal sectional view diagrammatically showing anapparatus for pulling a single crystal according to another embodimentof the present invention;

FIG. 8(a) is a front view diagrammatically showing a grasping part whichforms part of a single crystal holding means in the apparatus forpulling a single crystal according to the embodiment,

FIG. 8(b) is a side view thereof, and

FIG. 8(c) is a plan view thereof, and

FIG. 9 is a plan view diagrammatically showing the single crystalholding means which forms part of the apparatus for pulling a singlecrystal according to the embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The embodiments of the method of pulling a single crystal according tothe present invention are described below by reference to the Figures ofthe drawings. The method of pulling a single crystal according to thepresent invention are described on the assumption that a heavy singlecrystal having a large diameter of 12 inches or more is pulled.

FIG. 3 is a longitudinal sectional view diagrammatically showing anapparatus for pulling a single crystal. FIG. 4 is a partial sectionalside view diagrammaticallly showing a single crystal holding means whichforms part of the apparatus for pulling a single crystal and thevicinity thereof. FIG. 5 is a sectional view along line V--V of FIG. 4,and FIG. 6 is a plan view diagrammatically showing the single crystalholding means.

The apparatus for pulling a single crystal 10 has a single crystalholding means 11 by which a single crystal 26 having an enlarged portion26b and a reduced portion 26c under a neck 26a is pulled as the reducedportion 26c is held as shown in FIG. 3. The other parts thereof are thesame as those of the apparatus for pulling a single crystal 30 shown inFIG. 1. Accordingly, only the single crystal holding means 11 and theparts related thereto are described.

The single crystal holding means 11 includes a fitting portion 12, armportions 13a and 13b, supporting rods 14a and 14b, a supporting part 15,a disc 16 and guides 17, and is caused to wait in a prescribed positionuntil the single crystal 26 is pulled to a prescribed position.

The guides 17 are arranged on both sides of the inner walls of the lowerportion of a pull chamber 29a, and the disc 16 is placed on the guides17. The disc 16 does not move downward from the guides 17, but canfreely move upward. As shown in FIG. 6, the cylindrical supporting part15 is fixed to the central portion of the disc 16, and in the centralaxis portions of the disc 16 and the supporting part 15, through holes15a and 16a are formed, and are pierced by a pulling axis 24. In thesupporting part 15, two through holes 15b and 15c are horizontallyformed so as to pass through the central axis, which are pierced by twosupporting rods 14a and 14b. To these two supporting rods 14a and 14b,the upper end portions of bar-shaped arm portions 13a and 13b which arelocated almost in parallel and have bending portions 130a and 130b atthe lower ends thereof are screwed and fixed. To the bending portions130a and 130b at the lower end of the arm portions 13a and 13b, thefitting portion 12 in the shape of a "V" in a plan view is fixed asshown in FIG. 5. The arm portions 13a and 13b pierce the slightly bentand slender through holes 16b and 16c formed in the disc 16. The throughholes 16b and 16c have a bent shape in order to control the positions ofthe arm portions 13a and 13b. The arm portions 13a and 13b are formed inthe shape widening slightly outward from the positions where the throughholes 16b and 16c are formed, and can be temporarily fixed to the leftend portions 16b and 16c thereof or the right end portions 165b and 165cthereof in FIG. 6. Before pulling the single crystal 26 and for a periodof time from the beginning of the pulling, the arm portions 13a and 13bwait in the waiting positions of the end portions 160b and 160c as shownby virtual lines in FIG. 4. When the arm portions 13a and 13b hold thesingle crystal 26, they are transferred toward the end portions 165b and165c by pushing inward a press part 18 forming part of a press meansarranged at the lowest end of the pull chamber 29a and are located inthe reduced portion fitting positions. Here, the press part 18 canadvance with rotation in the horizontal plane in order to make itpossible to press even the arm portions 13a and 13b which are rotatedwith the pulling axis 24. By the above operation, the fitting portion 12fixed to the lower ends of the arm portions 13a and 13b is fitted to thereduced portion 26c formed in the single crystal 26 so that the singlecrystal 26 is held. Then, the single crystal holding means 11 is made tobe one with a holder 24a, the pulling axis 24 and associated parts wherethe single crystal 26 is held, and ascends as the pulling axis 24 ispulled.

The holder 24a and associated parts can be freely rotated and be pulledin the same manner as those in the conventional apparatus for pulling asingle crystal 30 (FIG. 1). The apparatus for pulling a single crystal10 has an optical measuring means 19 for measuring the diameter of thesingle crystal 26 in order to control the diameter of the pulled singlecrystal 26.

The method for pulling a single crystal using the single crystal holdingmeans 11 is described below. In the stage before the pulling of thesingle crystal 26, the single crystal holding means 11 is arrangedwithin a chamber 29. The arm portions 13a and 13b are temporarily fixedto the end portions 160b and 160c of the through holes 16b and 16c ofthe disc 16 so as to be in waiting positions. The pulling axis 24 passesthrough the through hole 15a of the supporting part 15 and the throughhole 16a of the disc 16, and the holder 24a holding a seed crystal 25 issuspended at the lower end of the pulling axis 24.

In the same manner as a conventional method, the seed crystal 25 isbrought into contact with a melt 23 within a crucible 21, and a neck 26ais formed under the seed crystal 25. While the diameter is measuredusing the optical measuring means 19, the pulling speed of the pullingaxis 24 is reduced so as to gradually increase the diameter, leading tothe formation of an enlarged portion 26b under the neck 26a. The pullingaxis 24 is pulled at a relatively high speed again, leading to theformation of a reduced portion 26c under the enlarged portion 26, andwhich has a smaller diameter than the enlarged portion 26b. Here, thereduced portion 26c is formed in the shape which makes it possible forthe fusion ring to be observed at all times using the optical measuringmeans 19. That is, as shown in FIG. 3. the reduced portion 26c is formedso that an angle θ_(s), which is formed by a straight line forming thesurface portion of the section of the reduced portion 26c and ahorizontal plane, is larger than an angle θ_(m), which is made by theoptical axis 19a of the optical measuring means 19 and a horizontalplane.

When the largest diameter of the enlarged portion 26b is D₁ and thelength of the segments Z forming the section of the reduced portion 26cwhich are lengthened to cross each other is L, the reduced portion 26cmay be formed so as to make tan θ_(s) expressed by Formula 1 larger thantan θ_(m). Formula 1:

    L/0.5D.sub.1 =2L/D.sub.1 = tan θ.sub.s.

Since the fusion ring can be observed at all times during the formationof the reduced portion 26c by forming the reduced portion 26c having theabove shape, the diameter thereof can be easily controlled. In addition,it is easy to cope with changes in the conditions such as thetemperature of the melt 23, and dislocation can be prevented from beinginduced to the reduced portion 26c.

After forming the reduced portion 26c, a shoulder 26d is formed bygradually reducing the pulling speed, and a main body 26e having auniform diameter is formed. When the holder 24a ascends to some extent,the holder 24a touches the disc 16 forming part of the single crystalholding means 11. Here, the length between the seed crystal 25 and thereduced portion 26c is controlled so that the fitting portion 12 is justfitted to the reduced portion 26c when the fitting portion 12 istransferred to the reduced portion fitting position. Accordingly, whenarm portions 13a and 13b and the fitting portion 12 are transferred fromthe waiting positions to the reduced portion fitting positions, thefitting portion 12 is fitted to the reduced portion 26c so as to holdthe single crystal 26. Even when the reduced portion 26c slightly slipsout of place, the reduced portion 26c can be held certainly since thefitting portion 12 has a "V" shape.

The holder 24a, pulling axis 24, and associated parts are made to be onewith the single crystal holding means 11. As the pulling axis 24 ispulled, the single crystal holding means 11 ascends at the same speed.By rotating the pulling axis 24, the single crystal holding means 11also rotates at the same speed. Therefore, the single crystal 26 may bepulled with the same conditions as those in the conventional case. Inthe pulling, since the single crystal 26 is held by the single crystalholding means 11, even a heavy single crystal 26 can be easily pulledwithout occurrence of troubles such as breakage. Even when the neck 26abreaks for some reason, the single crystal 26 does not fall since thesingle crystal 26 is held by the single crystal holding means 11, andthe pulling thereof can be continued safely in its original condition.

As described above, since the holder 24a and associated parts and thesingle crystal holding means 11 are made to be in one piece after theholder 24a touches the disc 16, the ascent/descent speed and the numberof revolutions are synchronized without any other operation. As aresult, there is no possibility that the central axis of the pullingaxis 24 is off that of the single crystal holding means 11. Since thestructure of the single crystal holding means 11 is relatively simple,troubles are not easily caused even in a high temperature atmosphere.

EXAMPLES AND COMPARATIVE EXAMPLES

The method of pulling a single crystal according to the invention aredescribed below in the Examples. As a comparison, the case wherein thediameter of the reduced portion is drastically reduced using the sameapparatus for pulling a single crystal as those used in Examples aredescribed below in the Comparative Examples using the apparatus forpulling a single crystal 10 shown in FIGS. 3-6.

Example 1 and Comparative Example 1

(Common conditions to Example 1 and Comparative Example 1)

                  TABLE 1                                                         ______________________________________                                        Dimension and weight of single crystal                                                            Length                                                      Sort of  (mm)  Material Number of                                             single Diameter under Weight weight pulls                                     crystal (mm) shoulder (kg) (kg) (times)                                     ______________________________________                                          P-type 300 1200 210 250 30                                                    silicon (12 in)                                                             ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Revolution                                                                      speed (rpm)  Conditions in chamber                                          Crystal Crucible   Flow of Ar (liter/min)                                                                      Pressure (Pa)                                ______________________________________                                          10 8 50 1330                                                                ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Dimension of                                                                    quartz crucible Dimension of heater                                         Diameter                                                                              Height   Inner       Outer    Height                                    (mm) (mm) diameter (mm) diameter (mm) (mm)                                  ______________________________________                                          750 470 800 850 600                                                         ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        Dimension of heat                                                               insulating mold  Dimension of chamber                                       Diameter Height      Inner      Height                                          (mm) (mm) diameter (mm) (mm)                                                ______________________________________                                          900 1300 1350 1200                                                          ______________________________________                                    

(Different conditions between Example 1 and Comparative Example 1)

                  TABLE 5                                                         ______________________________________                                        Dimension of each part of single crystal                                                         Enlarged portion                                                                           Reduced portion                               Neck           Largest          Smallest                                      Diameter   Height  diameter Height                                                                              diameter                                                                             Height                                 (mm) (mm) (mm) (mm) (mm) (mm)                                               ______________________________________                                        Ex-   3        150     40     40    10     50                                   ample 1                                                                       Com- 3 150 40 40 10 20                                                        para-                                                                         tive                                                                          Ex-                                                                           ample 1                                                                     ______________________________________                                    

The reduced portion 26c formed in Example 1 had a largest diameter D₁,of 40 mm, a smallest diameter D₂ of 10 mm, and a height of 50 mm asshown in Table 5. Accordingly, the length L was 66.7 mm, and accordingto Formula 1, tan θ_(s) was 3.35, which was larger than 2.144, thetangent (tan θ_(m)) of the angle which was made by the optical axis 19aof the optical measuring means 19 and a horizontal plane. As a result,during the formation of the reduced portion 26c, the diameter thereofcould be measured through the fusion ring and could be controlled.Therefore, the single crystal 26 having no fault or the like could bepulled, without induction of dislocation to the single crystal 26. Here,the fitting portion 12 was fitted to the reduced portion 26c just afterthe holder 24a touched the disc 16. Then, the single crystal 26 waspulled where the holder 24a and associated parts were made to be onewith the single crystal holding means 11. The neck 26a did not break inpulling and taking out the single crystal 26, so that the pulling couldbe safely performed. Furthermore, even when the neck 26a of the pulledsingle crystal 26 was artificially broken, the single crystal 26 did notfall. Thus, it was ascertained that the single crystal 26 was certainlyheld by the single crystal holding means 11.

On the other hand, in Comparative Example 1, the diameter of the reducedportion 26c was drastically reduced by increasing the pulling speedafter forming the enlarged portion 26. By the above operation, thereduced portion 26c having a largest diameter D₁, of 40 mm, a smallestdiameter D₂ of 10 mm, and L of 20 mm was formed. Therefore, the length Lwas 26.7 mm, and according to Formula 1, tan θ_(s) was 1.34, which wassmaller than tan θ_(m) of 2.144. Thus, during the formation of thereduced portion 26c, the diameter thereof could not be measured bymeasuring the fusion ring using the optical measuring means 19 and couldnot be appropriately controlled. As a result, dislocation was induced tothe pulled single crystals at a rate of 40%.

FIG. 7 is a longitudinal sectional view diagrammatically showing anotherapparatus for pulling a single crystal, FIG. 8(a) is a front viewdiagrammatically showing a grasping part which forms part of a singlecrystal holding means. FIG. 8(b) is a side view of the holding means,and FIG. 8(c) is a plan view of the holding means. FIG. 9 is a plan viewdiagrammatically showing the above single crystal holding means.

The apparatus for pulling a single crystal 60 has a single crystalholding means 61, by which a single crystal 26 having a fitting portion26g comprising an enlarged portion 26b and a reduced portion 26c under aneck 26a is pulled as the fitting portion 26g is grasped, as shown inFIG. 7.

The single crystal holding means 61, including grasping parts 62a and62b, a grasping part supporting disc 68, connecting parts 66a and 66b,and auxiliary supporting parts 65a, waits in a prescribed position untilthe single crystal is pulled to a prescribed position.

Guides 70 are arranged on both sides of the inner walls of the lowerportion of a pull chamber 29a, and the grasping part supporting disc 68is placed on the guides 70. The grasping part supporting disc 68 doesnot move downward from the guides 70 but can freely move upward. Asshown in FIG. 9, a through hole 68a is formed in the central axisportion of the grasping part supporting disc 68, which a pulling axis 24passes through. On both sides of the through hole 68a, through holes 68band 68c (which are slender in the transverse direction) are formedsymmetrically to the pulling axis 24. A through hole 68d which isslender in the vertical direction is formed perpendicularly to the lineconnecting the central axes in the transverse direction of the throughholes 68b and 68c.

The upper portions of arm portions 63a and 63b forming part of thegrasping parts 62a and 62b pass through the through holes 68b and 68c,and the grasping parts 62a and 62b are supported by the auxiliarysupporting parts 65a which are arranged on the arm portions 63a and 63bto support the arm portions 63a and 63b as if to put the grasping partsupporting disc 68 between the upper and lower sides. The arm portions63a and 63b can freely move right and left where they are supported bythe auxiliary supporting parts 65a. The grasping part 62a has a graspingportion 64a in the lower portion thereof whose inner shape almostcorresponds to the external shape of the fitting portion 26g as shown inFIG. 8. Thus, the fitting portion 26g is grasped as if to be wrapped bythe pair of grasping parts 62a and 62b arranged on both sides of thefitting portion 26g.

To the upper end of the arm portion 63a or 63b forming part of thegrasping part 62a or 62b, one end portion of a bar-shaped connectingpart 66a or 66b is fitted with a screw 65b so as to be rotatable. Theother ends of both the connecting parts 66a and 66b are fitted to aconnecting part supporting rod 66c (FIG. 7), which is fitted to thethrough hole 68d so as to be rotatable, and are connected. Theconnecting part supporting rod 66c can move freely inside the throughhole 68d.

Accordingly, when the arm portion 63a forming part of the grasping part62a is transferred toward the pulling axis 24, the connecting partsupporting rod 66c moves outward inside the through hole 68d. This makesthe arm portion 63b move toward the pulling axis 24 inside the throughhole 68c. The through holes 68b and 68c are formed symmetrically withrespect to the central axis, the connecting parts 66a and 66b arearranged symmetrically with respect to the line connecting the pullingaxis 24 and the central axis of the through hole 68d, and the armportions 63a and 63b are composed so as to always move symmetricallywith respect to the pulling axis 24.

Before pulling the single crystal 26 and for a period of time from thebeginning of the pulling thereof, the arm portions 63a and 63b wait inthe left and right end portions of the through holes 68b and 68c(waiting positions). When it is necessary to hold the single crystal 26,by pushing inward a press part 69 forming part of a press means arrangedin the lower portion of the pull chamber 29a, the arm portions 63a and63b are transferred to the end portions close to the pulling axis 24 ofthe through holes 68b and 68c, which are the fitting portion graspingpositions. At that time, the connecting part supporting rod 66c movesoutward in the through hole 68d and when it reaches the outside endportion, a fixing part 68e fitted to springs 68f functions. Therefore,the connecting part supporting rod 66c is fixed and the arm portions 63aand 63b are also fixed.

By the above operation, the single crystal 26 is held by grasping thefitting portion 26g formed in the single crystal 26 as if to wrap itfrom both sides by the grasping portions 64a and 64b arranged at thelower ends of the arm portions 63a and 63b. Then, the single crystalholding means 61 is made to move as one piece with the holder 24a,pulling axis 24, and associated parts where the single crystal 26 isheld, and ascends as the pulling axis 24 is pulled.

A method for pulling a single crystal using the single crystal holdingmeans 61 is described below. In the stage before the pulling of thesingle crystal 26, the single crystal holding means 61 is arranged in achamber 29, and the arm portions 63a and 63b are located in the left andright end portions of the through holes 68b and 68c (waiting positions).The pulling axis 24 passes through the through hole 68a of the graspingpart supporting disc 68, and at the lower end of the pulling axis 24,the holder 24a holding the seed crystal 25 is suspended. The holder 24aand associated parts can be freely rotated and pulled in the same manneras those in the conventional apparatus for pulling a single crystal 30(FIG. 1).

The seed crystal 25 is brought into contact with the melt 23 filling thecrucible 21 so as to form the neck 26a under the seed crystal 25. Byreducing the pulling speed of the pulling axis 24, the diameter isgradually increased so as to form the enlarged portion 26b under theneck 26a. Consecutively, by pulling the pulling axis 24 at a relativelyhigh speed again, the diameter is gradually reduced so as to form thereduced portion 26c.

After forming the enlarged portion 26b and reduced portion 26c (fittingportion 26g), by reducing the pulling speed gradually, the shoulder 26dis formed, and the main body 26e having a uniform diameter is formed.When the holder 24a ascends to some extent, the holder 24a touches thegrasping part supporting disc 68 which forms part of the single crystalholding means 61. At that time, the length from the seed crystal 25 tothe fitting portion 26g is controlled so that by transferring thegrasping portions 64a and 64b to the fitting portion grasping positions,the grasping portions 64a and 64b just grasp the fitting portion 26g. Asa result, when the arm portions 63a and 63b, and the grasping portions64a and 64b are transferred from the waiting positions to the fittingportion grasping positions using the press part 69, the graspingportions 64a and 64b grasp the fitting portion 26g, so that the singlecrystal 26 is held.

Then, the holder 24a, pulling axis 24, and associated parts are made tomove as one piece with the single crystal holding means 61. As thepulling axis 24 is pulled, the single crystal holding means 61 ascendsat the same speed. By rotating the pulling axis 24, the single crystalholding means 61 rotates at the same speed. Accordingly, then, thesingle crystal 26 may be pulled with the same conditions as those in aconventional method. In the pulling, since the single crystal 26 is heldby the single crystal holding means 61, even a heavy single crystal 26can be easily pulled without occurrence of troubles such as breakage.Even when the neck 26a breaks for some reason, the single crystal 26does not fall since the single crystal 26 is held by the single crystalholding means 61, and the pulling can be continued safely in itsoriginal condition.

As described above, since the holder 24a and associated parts and thesingle crystal holding means 61 are made to move as one piece after theholder 24a touches the grasping part supporting disc 68, theascent/descent speed and the number of revolutions are synchronizedwithout any other operation. Thus, there is no possibility that thecentral axis of the pulling axis 24 is off that of the single crystalholding means 61. Since the structure of the single crystal holdingmeans 61 is relatively simple, troublles are not easily caused even in ahigh temperature atmosphere.

Example 2

The single crystal 26 was pulled by the method described in the aboveembodiment. The conditions are shown in Tables 6-10.

                  TABLE 6                                                         ______________________________________                                        Dimension and weight of single crystal                                                            Length                                                      Sort of  (mm)  Material Number of                                             single Diameter under Weight weight pulls                                     crystal (mm) shoulder (kg) (kg) (times)                                     ______________________________________                                          P-type 300 1200 210 250 30                                                    silicon (12 in)                                                             ______________________________________                                    

                  TABLE 7                                                         ______________________________________                                        Revolution                                                                      speed (rpm)  Conditions in chamber                                          Crystal Crucible   Flow of Ar (liter/min)                                                                      Pressure (Pa)                                ______________________________________                                          10 8 50 1330                                                                ______________________________________                                    

                  TABLE 8                                                         ______________________________________                                        Dimension of                                                                    quartz crucible Dimension of heater                                         Diameter                                                                              Height   Inner       Outer    Height                                    (mm) (mm) diameter (mm) diameter (mm) (mm)                                  ______________________________________                                          750 470 800 850 600                                                         ______________________________________                                    

                  TABLE 9                                                         ______________________________________                                        Dimension of heat                                                               insulating mould  Dimension of chamber                                      Diameter Height      Inner      Height                                          (mm) (mm) diameter (mm) (mm)                                                ______________________________________                                          900 1300 1350 1200                                                          ______________________________________                                    

                  TABLE 10                                                        ______________________________________                                        Dimension of each part of single crystal                                                       Enlarged portion                                                                            Reduced portion                                Neck         Largest           Smallest                                       Diameter                                                                              Height   diameter Height diameter                                                                             Height                                  (mm) (mm) (mm) (mm) (mm) (mm)                                               ______________________________________                                          3 100 40 30 10 50                                                           ______________________________________                                    

Results of Example 2

The neck 26a did not break in pulling and taking out the single crystal26, so that the pulling could be safely performed. When the neck 26a ofthe pulled single crystal 26 was artificially broken, the single crystal26 did not fall. Thus, it was ascertained that the single crystal 26 wascertainly held by the single crystal holding means 11.

Industrial Applicability

The method and the apparatus for pulling a single crystal according tothe present invention are effective in safely and efficientlymanufacturing a single crystal to which dislocation is not induced.

What is claimed is:
 1. A method of pulling a single crystal,comprising:dipping a seed crystal into a melt within a crucible; pullingthe dipped seed crystal at a controlled rate so as to control a size ofa diameter of the single crystal; forming a neck of the single crystalunder the dipped seed crystal by rotating the dipped seed crystal as thedipped seed crystal is pulled; gradually increasing the diameter of thesingle crystal after said forming of the neck so as to form an enlargedportion of the single crystal having a gradually increasing diameter;gradually reducing the diameter of the single crystal after said gradualincreasing of the diameter so as to form a reduced portion of the singlecrystal having a gradually decreasing diameter; and measuring thediameter of the single crystal at the interface between the melt and thesingle crystal by using an optical measuring device arranged above thecrucible, wherein the optical measuring device is arranged above thecrucible such that the optical axis and a horizontal plane form an angleθ_(m) ; wherein said gradually reducing the diameter of the singlecrystal comprises measuring the diameter of the reduced portion at alltimes using the optical measuring device, and comprises reducing thediameter such that a straight line along a surface of the reducedportion and a horizontal plane form an angle θ_(s), whereby θ_(s) isgreater than θ_(m).
 2. The method of claim 1, wherein said graduallyincreasing the diameter of the single crystal comprises pulling the seedcrystal at a gradually decreasing rate.
 3. The method of claim 2,wherein said gradually reducing the diameter of the single crystalcomprises pulling the seed crystal at a gradually increasing rate. 4.The method of claim 1, wherein said gradually reducing the diameter ofthe single crystal comprises pulling the seed crystal at a graduallyincreasing rate.